1. Field of the Invention
The present invention relates generally to an access method and a system therefor in a wireless communication system, and more particularly to a multiple access method and a system therefor in a wireless communication system using at least two multiple access techniques.
2. Description of the Related Art
In its initial stage, a wireless communication system was developed to support the mobility of users and provide a voice communication service. As technology advances, a wireless communication system capable of providing a data communication service as well as the voice communication service has been commercialized. The current mobile communication technology called “third generation” is mainly divided into a 3GPP2 standard for synchronous systems and a 3GPP standard for asynchronous systems. The third generation technology is based on the voice communication service in terms of the traffic type but it is under study and development, focusing more on a multimedia service.
The 4G mobile communication system, which will be provided in the near future, needs to have improved system performance over the 3G mobile communication system. One of the most important requirements for the 4G mobile communication system is the ability to provide a multimedia service at a high rate. Efficient use of frequencies is necessary to meet this requirement. Additionally, high Quality of Service (QoS) must also be guaranteed in various channel environments.
The 3G mobile communication system uses Adaptive Modulation & Coding (AMC) or water filling per subcarrier in order to transmit data at a high rate in a limited frequency band. Although the AMC or water filling technique can increase the frequency efficiency, these techniques can only be used under certain conditions.
For example, the technique requires real-time channel state information. Also, channel feedback is required in a Frequency Division Duplexing (FDD) mode. A large amount of information is required for complete feedback transmission of rapidly varying channels. If the complete feedback transmission is not performed, channel states varying in real time cannot be reflected in the system. Additionally, if a mobile terminal moves at a high speed, the channel variation thereof increases. This makes appropriate use of the AMC technique difficult.
Accordingly, the AMC and water filling techniques can be effectively used to increase frequency efficiency for channels that require no channel feedback, differently from the frequency division duplexing mode. That is, the techniques can be used in environments in which channel feedback information can be obtained with a minimum load.
Also, as the terminal moves more slowly, algorithms for the AMC and water filling techniques can be applied more effectively. In these conditions, the AMC and water filling techniques can provide high rate data transmission with higher frequency efficiency.
However, the increase of frequency efficiency is needed to transmit a large amount of data in the mobile communication environment. A frequency reuse factor needs to approach one to increase the frequency efficiency. Interference between neighboring cells must be suppressed to bring the frequency reuse factor near one. Some examples of the method for suppressing the interference are interference avoidance and interference averaging.
The AMC and water filling based techniques, which can increase the frequency efficiency, bring about no synergy with the interference avoidance technique that can bring the frequency reuse factor near one.
As indicated above, the next generation wireless communication system requires higher rate data transmission. Effective use of frequencies is necessary to transmit data at a higher rate. However, the conventional techniques, including ones currently in development, provide no solution for highly effective use of frequencies.